Inflatable restraints or airbags have been shown to reduce the seriousness of occupant injury during an automobile crash. An airbag, filled with inflation gas, provides a cushion between a vehicle occupant and the instrument panel or steering wheel. The likelihood of injury is minimized by the airbag absorbing some or all of the kinetic energy associated with the occupant during a crash.
An inflator provides the inflation gas utilized to inflate an airbag. Inflators generally provide inflation gas by burning a pyrotechnic material, releasing stored gas, or by some combination thereof. During a crash, the inflator is actuated to rapidly inflate an airbag. The aggressive airbag deployment has the advantage of getting the inflated airbag in front of the vehicle occupant as soon as possible. The problem associated with aggressive airbag deployment is the possibility of a child, a small adult, or an out of position adult interacting with the airbag while it is being inflated. Out of position is a phrase utilized in the safety restraint industry that refers to an occupant that is not sitting properly in his/her seat or sitting too close to the airbag module.
Dual stage inflators have been developed to reduce the injury to small adults or children by reducing the aggressiveness of airbag deployment. These inflators provide varying output levels of inflation gas in accordance with the size and position of the occupant. The dual stage inflators are able to provide a full output of inflation gas to protect a full size occupant who is not out of position. The dual stage inflator is also able to provide a staged output of inflation gas for the occupants who are smaller in size or out of position. The staged output deployment operates by providing a portion of inflation gas to partially inflate the airbag and after a period of time, the inflator provides more inflation gas to fill the airbag.
Dual stage inflators have been shown in the past. The dual stage inflators shown in U.S. Pat. No. 6,189,922 B1 and U.S. Pat. No. 6,168,200 B1 have a first and second gas generant. Another variation of the dual stage inflator has two separate burst disks which is illustrated in U.S. Pat. Nos. 5,022,674, 5,351,988, and 5,016,914.